1. Field of the Invention
The present invention relates to a calibration apparatus and a calibration method that calibrate an optical measurement apparatus that measures, as an amount of scattering and absorption of light, information related to an internal structure of an object to be measured.
2. Description of the Related Art
Conventionally, backward scattered returned light from a comparatively weak scattering medium such as body tissue has been known to be observed as light that increases interference according to a degree of spatial coherence of illumination light thereof (see Young L. Kim, et. al: Low-Coherence Enhanced Backscattering; Review of Principles and Applications for Colon Cancer Screening, Journal of Biomedical Optics, 11(4), 041125 2006). A technique of measuring spectroscopic information using this phenomenon is called low-enhanced backscattering spectroscopy (LEBS), and characteristics of an interference pattern with respect to a scattering mean free path (a reciprocal of a scattering coefficient) in a scattering medium have been well studied (see V, Turzhitsky, et. al: Characterization of Light Transport in Scattering Media at Subdiffusion Length Scales with Low-Coherence Enhanced Backscattering, IEEE journal of selected topics in quantum electronics, Vol. 16, No. 3, 619 (2010)). This scattering mean free path has a correlation with an internal structural change in the scattering medium and is used in detecting a minute tissue structural change as seen in early cancer. For example, distinguishment of colorectal cancer using an interference pattern of scattered returned light has been known to be possible (see Hemant K. Roy, et. al: Association Between Rectal Optical Signatures and Colonic Neoplasia: Potential Applications for Screening, Cancer Research, 69(10), 4476 (2009)).
A technique of applying the above mentioned LEBS to noninvasive measurement within a body through a small diameter probe inserted in an endoscope is known (see U.S. Patent Application Publication No. 2009/0009759). In this technique, in order to obtain an interference pattern, detection fibers are arranged at different plural positions in a plane on which the interference pattern is formed, and signals are detected by detectors corresponding to the respective detection fibers.